A peasant/slave who is connected to the land.  Whoever owns the land, controls the serfs on it.  This is an important cog in the machinery of feudalism. 

The rejection and/or destruction of religious imagery thought to be heretical because it constituted the worship of false idols.  The disagreement on whether these images was allowed would lead to the Great Schism, the break between the Roman Catholic (who allowed religious imagery) and Eastern Orthodox Church (who forbid it).

Ordered by Pope Urban II, these series of wars A) gave European's a common enemy and goal, leading to less fighting within the borders of Christendom and B) led to increasing cultural connection with the Arab world, which had preserved Greco-Roman thought and classics. The reintroduction of these themes would lead to the rebirth of European culture in the form of the Renaissance.  

Through conquests and treaties this man would temporarily recapture the idea of a united Rome, being named Holy Roman Empire on Christmas Day of 800 C.E.  His empire would fall apart after his death but within it's borders the countries of France, Austria, and Germany would get their start.  

This pivotal battle in 732 C.E., won by the Frankish leader, Charles Martel, would stop Muslim conquerers from moving into Western Europe, effectively keeping Europe Christian rather than letting Islam spread into Europe as it spread almost everywhere else.  

Known for their fearsome raiding reputation, these brave seafarers would eventually settle throughout Europe from Ireland, Normandy (France), down the Volga River into Russia (why some Russians have blonde hair), and even as far as the Americas (centuries before Columbus got there).  

As the capital of the Byzantine Empire, this city of many other names lay strategically on the Bosporus, the little strip of water separating Europe and Asia in modern-day Turkey.  This position was easily defensible meaning that the city, and the Byzantine Empire it represented, would act as a barrier between Islam and Southern and Eastern Europe, allowing the world of Christendom to recover from the fall of the Roman Empire and develop separate from Islam.  It wouldn't fall to the Ottoman Turks (the Sword of Islam) until 1453. 

A pyramid shaped hierarchical structure, it was the dominant social system in medieval Europe, in which the nobility held lands from a king in exchange for military service, and vassals were in turn tenants of the nobles, while the peasants (serfs) were obliged to live on their lord's land and give him homage, labor, and a share of the produce in exchange for military protection.

While it served to protect Christian Europe from Muslim conquest, this once proud empire was ultimately weakened by constant warfare with the Persian Sassanid Empire and Turks while Venice and Genoa took over it's trade networks, and Crusaders weakened its security by using it as a base against Muslims in the Holy Land.